1. Field of the Invention
The present invention generally relates to plastic wheel covers with integral retention systems. More specifically, this invention is directed to an ornamental wheel cover that is easily attachable and removable, that is inexpensive, and that has a wire retention device to provide improved wheel cover retention.
2. Description of the Related Art
Related art references have suggested various methods and apparatuses for removably attaching a wheel cover to a wheel. For example, U.S. Pat. No. 4,123,111 to Renz et al. discloses a retaining cover that is provided circumferentially in the engaging plane of the lug nuts with detents to engage the outer periphery of the lug nuts. The retaining cover has a shape that differs from the circular shape of the wheel cover exhibiting a relatively large lever arm between the connecting lines of the points of engagement of the lug nuts, thereby reducing the spring rate. The lug nuts are seated in recesses in the peripheral edge of the retaining cover. The edge of the retaining cover snaps in within the area of the recesses. To cover the lug nuts a wheel cover cap is provided that is mounted over the retaining cover.
Several problems exist with the Renz et al. device. Plastic is a relatively low strength material which tends to relax and/or creep over time and with temperature. Therefore, removal and replacement of the retaining cover could lead to loss of retention of the retaining cover to the lug nuts. The retaining cover is subject to stress and flexing in an area that is recessed and has a much thinner material thickness than the surrounding area of the cover, thereby making it subject to cracking. Thermal expansion rates between the steel lug nut and plastic cover differ aggravating the above stated problems. Further, the fact that Renz et al. require a relatively large lever arm between the connecting points of engagement and the detent points in order to reduce the spring rate, it would not be possible to obtain this arrangement with shallow profile wheel covers. Further, the two-piece assembly provides large cavities between the retaining cover and the outer wheel cover in which mud and road debris can collect over time.
U.S. Pat. No. 4,382,635 to Brown et al. attempts to overcome some of these problems by disclosing a wheel cover with integral retention fingers which is useable on conventional steel wheels. The cover is integrally retained on the wheel by the cooperating inter-engagement of tubular extensions of the cover mounting to the lug nuts. The extensions are axially slotted so as to be divided into a plurality of cantilevered fingers which cooperate with the lug nuts to retain the wheel cover thereto. The fingers of each extension include integral radially extending abutments which resiliently engage within a radial opening groove of a respective lug nut to resiliently grip the nut and retain the cover thereto. Concurrent with receipt of the abutments in the groove, a tapered radial face on each finger engages an axially outwardly extending annular face of the apertured embossment in an attempt to provide a slight axial outward force on each finger to prevent axial shifting movement of the extensions relative to the lug nuts.
The abutments describe a circle which is slightly less than the circle of the hexagonal portion of the lug nuts so that the fingers slightly separate or flex axially outwardly as the abutments move over the hexagonal portion of the lug nuts. Therefore, the fingers separate as the abutments move over an annular rib of the lug nuts until the abutments snap into the circumferential groove in each respective lug nut. When the abutments are received in the groove, the fingers return substantially to their normal position. A radial tapered face of each abutment engages an axially outwardly extending annular face of the wheel surface to provide a slight axial outward force on each extension to prevent axial shifting movement of the extensions relative to the lug nuts.
One of several problems associated with this design is the adverse effects of tolerance stack-ups between the axially outwardly extending annular face and the location of the groove on the lug nut. The fit of the cover to the lug nut depends on the depth and width of a groove that is on the lug nut and a tapered surface on the wheel face next to where the lug nut is seated. The tolerance build up among the radial tapered extension on the end of each finger of the cover, the lug nut, and the taper on the wheel's surface results in groove width variations that will prevent the radial tapered face of the abutment to move to the bottom of the groove, resulting in a loose fit on the lug nut and a stress condition in the fingers of the retainer, thereby subjecting the retainer to the previously described problems regarding the use of plastic.
Another problem associated with the lack of positive positioning in the Brown design is the potential for improper installation. It is possible, during attachment of the cover to the wheel, to apply a force that causes the cover to overtravel and press the fingers against the tapered wheel surface which in turn opens up the fingers, forcing them out of the groove and causing them to travel along the tapered wheel surface, which results in a loose fit.
Yet another drawback of the Brown design is a potential problem with the location of the circumferential groove on the lug nut and improper torque on aluminum wheels. It is known in the art that in order to achieve proper torque on the lug nuts for aluminum wheels, the conical seat must be deeper, providing more surface area contact with the wheel surface than required for steel wheels. The groove in the lug nut of the Brown design will prevent the lug nut from seating properly on an aluminum wheel by presenting less surface area contact with the aluminum wheel and thereby making it a problem to achieve sufficient torque for an aluminum wheel. In other words, the lug nut in the Brown design is not compatible with both steel and aluminum wheels.
As a solution to some of the above disadvantages, U.S. Pat. No. 5,163,739 to Stanlake teaches a wheel cover that includes a plurality of integral tubular extensions for attaching the wheel cover to the lug nuts of the wheel. Each tubular extension has a plurality of slots extending axially from the wheel cover wherein the slots define a plurality of fingers that axially engage an annular rib of a respective lug nut. The fingers include an undercut portion to accommodate a one-piece wire band retainer having a plurality of circumferentially expanding rings and a plurality of concave bends. Alternatively, a split ring wire retainer may also be used.
The wire band retainer is pushed onto the integral tubular extensions such that the fingers flex radially inward and the circumference of the rings increase to encircle the fingers of the extensions and be received by the undercuts. The increase in the circumference of the rings is facilitated by the concave bends of the retainer flexing to a straightened position. Accordingly, Stanlake teaches a retention apparatus whereby the tubular extensions of the wheel cover are completely encircled by the wire band retainer to limit the outward radial movement of the flexible fingers and to bias the flexible fingers into engagement with the lug nuts.
While the incorporation of the wire retainer addresses some of the problems associated with conventional plastic wheel covers, there are several difficulties with the Stanlake invention. The wheel cover taught by Stanlake can only be removed from the wheel by first removing the lug nuts which is a difficult and time consuming process as compared with conventional snap-fit plastic wheel covers. Furthermore, the wheel cover is limited to wheel applications in which it is desirable to have exposed lug nuts as access thereto is essential. Finally, the configuration taught by Stanlake, in which a one-piece wire band retainer encircles the perimeter formed collectively by the lug nuts, encircles each lug nut individually, and provides for a plurality of concave bends requires excessive wire material thereby incurring unnecessary material cost.
Because of the various problems identified with prior art retention systems, there is a need for a wheel cover having an integral fastening system that provides positive positioning of the cover relative to the wheel thereby eliminating the effects of tolerance stack-ups and the possibility of overtravel that result in poor fit of the cover to the wheel. There is also a need for a decorative wheel cover that is capable of covering the central portion of a wheel, including the lug nuts, that is easily attachable and removable, that maintains retention in high temperature environments, and that maintains retention after repeated attachment and removal. The cover attachment must not affect the lug nut torque or the contact interface between the lug nut and the wheel surface area so that a standard lug nut can be used for both aluminum and steel wheels.